The present invention relates generally to systems and methods for transmitting data. More specifically, the present invention relates to improved jitter processing and multiplexing of video data.
There are presently a variety of different communication channels for transmitting or transporting video data. For example, communication channels such as coaxial cable distribution networks, digital subscriber loop (DSL) access networks, ATM networks, satellite, terrestrial, or wireless digital transmission facilities are all well known. Many standards have been developed for transmitting data on the communication channels. For the purposes herein, a channel is defined broadly as a connection facility to convey properly formatted digital information from one point to another. A channel includes some or all of the following elements: 1) physical devices that generate and receive the signals (modulator/demodulator); 2) medium that carries the actual signals; 3) mathematical schemes used to encode and decode the signals; 4) proper communication protocols used to establish, maintain and manage the connection created by the channel 5) storage systems used to store the signals such as magnetic tapes and optical disks. The concept of a channel includes but is not limited to a physical channel, but also logical connections established on top of different network protocols, such as xDSL, ATM, IP, wireless, HFC, coaxial cable, Ethernet, Token Ring, etc.
The channel is used to transport a bitstream, or a continuous sequence of binary bits used to digitally represent video, audio and/or data. Since transmission of video data with existing communication channels is often excessive, compression is an approach used to make digital video images more transportable. Digital video compression allows digitized video data to be represented in a much more efficient manner and makes it possible to transmit the compressed video data using a channel at a fraction of the bandwidth required to transmit the uncompressed video data. Compression represents significant data savings, which results in much more efficient use of channel bandwidth and storage media.
To further reduce the transmission load, bitstreams are frequently combined for transmission within a channel. A multiplex is a scheme used to combine bitstream representations of multiple signals, such as audio, video, or data, into a single bitstream representation. A multiplexer then refers to an apparatus or software that multiplexes multiple bitstreams using a suitable multiplex scheme. A re-multiplex is one class of multiplexing and refers to a scheme used to combine bitstream representations of multiple multiplexed signals, such as multiple video signals, into a single bitstream representation. A re-multiplexer then re-multiplexes data from multiple multiplexed bitstreams into a single bitstream.
Multiplexing schemes usually vary the bandwidth allocated to each incoming bitstream, or its associated channel, based on the output channel bandwidth and current bitstream demands. One problem with delivering real-time compressed video bitstreams over a given bandwidth channel is matching the available bandwidth to the compressed bit rate of the data being transmitted. If the channel bandwidth is not enough, rate reduction is used to decrease the bandwidth required to send the compressed video data. The rate reduction may include re-quantization with a larger quantization step value or complete re-encoding, for example. After suitable rate reduction, the multiplexer or re-multiplexer then schedules the packets for transmission. Rate reduction often diminishes end-user video quality. Since rate reduction often leads to picture quality degradation, it should be minimized. However, many conventional transmission systems produce excessive rate reduction, leading to diminished output video quality.
Based on the foregoing, improved methods and systems for transmitting video data that reduce the amount of rate reduction would be desirable.